Field of the Invention
This invention relates generally to an apparatus for casting a portion of a the or other article of manufacture, and, more specifically, to an apparatus that has a gate design that has a circular runner and concentric channel or waste reservoir for separating off-ratio material before it enters the cavity that forms a portion of the tire or other article of manufacture. The design may further include a passage that connects the runner to the waste reservoir as well as an air vent that allows trapped gas or air to exit the waste reservoir as it fills with waste material, a valve that is operatively associated with the passage for closing and opening the passage at appropriate times, and a nozzle for initially introducing material into the waste reservoir and subsequently into the runner.
Description of the Related Art
An emerging field in tire development involves the manufacture and use of non-pneumatic or hybrid tires that do not depend solely on gas to support the tire structurally as these tires are not prone to deflation, which can render standard pneumatic tires inoperable, An example of such a tire is disclosed by U.S. Pat. No. 7,201,194, which is commonly owned by the applicant of the present application. The content of this patent is incorporated herein by reference for all purposes hi its entirety. In an exemplary embodiment of the '194 patent, the nom-pneumatic tire includes an outer annular shear band and a plurality of web spokes that extend transversely across and radially inward from the annular shear band and are anchored in a wheel or hub. In certain embodiments, the annular shear band may further comprise a shear layer, at least a first membrane adhered to the radially inward extent of the shear layer and at least a second membrane adhered to the radially outward extent of the shear layer. In addition to the ability to operate without a required inflation pressure, the invention of U.S. Pat. No. 7,201,194 also provides advantages that include as more uniform ground contact pressure throughout the length of the contact area. Hence, this tire mimics the performance of a pneumatic tire.
FIG. 1 shows such a tire that defines a radial direction R. For reference, all the reference numerals, in the 100's used herein refer to the tire features while all reference numerals in the 200's used herein refer to a molding apparatus for making such a tire and reference numerals in the 300's used herein refer to features of a gate, runner and waste reservoir design according to a first embodiment of the present invention and reference numerals in the 400's used herein refer to a features of a second embodiment of the present invention. The tire 100 comprises a tread 102 that is attached to the outward extent 104 of the spokes 106, which in turn, are connected to a hub or wheel 108 at their inward extent 110 by means known in the art such as by molding spokes between the hub 108 and the tread 102, which have been prepared for suitable bonding to the polyurethane. An outer annular band 105 is located between the outward extent of the spokes and the tread and an inner annular band 107 is found at the inward extent of the spokes, connecting them together. This inner annular band 107 can be used to attach the tire to a hub or wheel.
For the version of the tire 100 shown, the annular bands 105, 107 and spokes 106 are formed by pouring a polyurethane liquid into a rotational mold where the liquid is spread via centrifugation and then cured or hardened (see published patent application WO 2012094005 A1 for an example). It can also be seen that the spokes 106 are grouped in pairs and that the individual spokes 106′, 106″ within each pair are consistently spaced from each other and that each pair is spaced consistently from the adjacent pair around the circumference of the tire. The spacing within each pair and the spacing between each adjacent pair do not need to be the same. As described by the Abstract and col. 2, lines 28-41 of the '194 patent, the spokes 106 support the tire 100 in tension near the top of the tire 100 and not in compression. Instead, the spokes 106 at the bottom of the tire near the contact patch, which is where the tread 102 of the tire 100 contacts the road, compress or buckle easily. This helps the tire to simulate the pneumatic support function of a pneumatic tire.
Due to the sensitive and important function that the annular bands 105, 107 serve, i.e. to create the bond between the tread and the hub or wheel, as well as aesthetic concerns, it is desirable that the thickness of the bands remain constant. Looking at FIG. 2, mold cores 238″ found on a bottom mold half 234 are shown that form the spokes and inside surfaces 101 of the annular bands. These mold cores are drafted on the surfaces 237 that form the spokes themselves as mold cores coming from one side of the mold interarticulate with similarly configured mold cores coming from the other half so that the thickness of the spokes can remain constant even if there is draft present. However, these mold cores are undrafted on the surfaces 235 that form the inside surfaces of the annular bands. In the case of the inside surface of the outer annular band 105, the inside surface of the tread is substantially cylindrical, requiring that the inside surface of the outer annular band also be cylindrical to maintain the thickness of the annular band and to avoid aesthetic inconsistencies on the outer annular band from one side of the tire to the other. A similar situation exists for the inside annular band.
Due to the structural requirements of the spokes and the annular bands, it is preferable that they be aimed without bubbles, sinks, voids, or other molding or casting defects as these can deleteriously affect the performance of the tire. Also, it is desirable that the quality of the polyurethane that forms these portions of the tire be good so that once cured, these structures do not fail when the tire is used. In other words, the tire's spoke structure and annular bands require that all the polyurethane used in these areas meets minimum properties. Polyurethane dispensed from most commercially available machines or mixheads today inherently output initially some amount of poor quality or off-ratio material for a short period of time at the beginning of the shot. This results in the initial part of the shot being discarded. Typically, this is done by dispensing the material into a separate container outside of the mold and then while dispensing, moving the injection nozzle back over the mold cavity, which can be messy.
Additionally, when using low pressure mixheads, as the mixhead is moved after dispensing a shot, there is a problem with dripping polyurethane as the mixhead moves away from the mold. This happens since these mixheads have nozzles that are gravity fed and that lack a shutoff valve. In applications where there is some type of valve associated with the mixhead that is used for filling the mold, such as when a ball valve is employed, the flow is momentarily stopped or dead headed, resulting in disruption in the flow, which causes metering inaccuracy of the dispensing machine. That is to say, the ratio of material components is undesirably impacted and thus inaccurate.
Yet another problem with using commercially available injection systems is that when the gate is below the final level of polyurethane, as is the case when a bottom fill scheme is used, there is a need to prevent backflow from the mold cavity through the gate and back through the feed system.
Accordingly, it is desirable to find an apparatus and method that allows such tires or other articles of manufacture to be made using a feed system that allows polyurethane or other material to be fed into a mold cavity after the poor quality material has been separated and discarded without necessitating movement of the mixhead, dripping of the material or any other type of mess. It would be particularly useful if such an apparatus and method could be designed that prevented backflow through the gate after the mold cavity has been filled. Finally, it would be ideal if the proposed apparatus and method could be used with rotational or non-relational casting or molding.